The use of polyurethanes as foams and the like in the building industry has been gaining popularity. For example, one of the efforts which the industry has capitalized on in recent years has been the development of a rigid polyurethane foam which has flame retardance and generates less smoke when it does burn.
Polyurethanes are formed by the reaction of polyisocyanates and polyols. The term "polyol" is used by those in the art to refer to organic compounds containing two or more hydroxyl groups although typical commercially available polyols commonly have hydroxyl numbers in the range of 300 to 500 and higher.
Such commercially available polyols typically contain concentrations of alkali and/or alkaline earth metals, e.g. sodium potassium and calcium in the form of hydroxides which are used as catalysts to form the polyols. Before the polyols are used to form polyurethanes it is desirable to remove as much of the residual alkali or alkaline earth metal catalyst as possible from the polyol. This is because such alkali and alkaline earth metals as sodium, potassium and calcium are also used as catalysts in polyurethane formation and if they are not removed from polyols before the polyols are reacted with polyisocyanates a premature reaction leading to the formation of hard, brittle polyurethanes of undesirable chemical and physical properties can easily occur.
The common practice has been to use magnesium silicates to remove alkali and alkaline earth metals from polyols. While magnesium silicate does an adequate job of adsorbing the metals from the polyol, its use has proven to be disadvantageous due to the fact that commercially available magnesium silicates are very fine and therefore have poor filtration characteristics when one attempts to remove these very fine materials from polyols.
What is needed, therefore, is a process which is economical and yet efficiently and effectively removes at least substantially all of the alkali and alkaline earth metal catalysts from polyols before the latter are used to form polyurethanes.